Hijikata: If u see any suspicious - looking people, don't hesitate to take them down. I'll take responsibility.
Okita: Really? Then if I see a samurai, I'll kill him, and u can take the consequences.
Hijikata: Okay, everyone, forget what I just said.

When Gin and the others thought they were chased by that green-big body alien! The quotes are so damny funny!
Here are some:
Kagura: Shut up! Just say we'll live for him too!
Gin-chan: My life comes before the earth!
and then the episode when Sadaharu got bigger and bigger
Sadaharu to Kagura : You just got the fifth rank in Gintama polling and Kagura went crazy! That's soooo hilarious! And also when Okita says, "You're arrested for interfering public safety and breaking a police afficer's heart!

"It's dangerous, so please step back. You'll end up like this person. He puts on a poker face, but it really, really hurts. It's embarassing." -Sougo

Sougo- "Hijikata-san. I forgot my flute at the headquarters so i'm gonna go back and get it really quick."
Hijikata- "Right be sure to not come back again. Damnit i'm sick of you guys, it's enough! I'll go alone so wait there, you bastards."
[walks towards the burning building and the Neo Armstrong Cyclone Jet Armstrong Cannon pops out of the building]
Hijikata- "Sougo, I forgot the protractor at the headquarters, so i'm gonna go back and get it really quick."
Sougo- "Hijikata-san, it's ok. If you want a protractor I have one right here."